How to avoid losing media when working with iCloud Photo Library

I may have noted before that we receive more questions about
Photos for macOS than any other topic at Mac 911. A recent set
of questions from Macworld reader Pedro bring up an interesting
intersection of potential pitfalls, some of which I’ve answered
individually before, but which are useful to look at together.

Pedro has a small disk drive on his MacBook Air, just 128GB,
and thus is wrestling like many people with keeping his entire
Photos library on the internal drive. He has iCloud Photo
Library active, and wants to rely on it, but is already running
out of space. He has three questions.

Syncing, disabling, deleting, and then
Pedro knows that deleting an image off the
laptop will delete it everywhere when iCloud Photo Library is
active, something I’ve reminded readers of
time again
. That’s good to know. However, he wonders about
this scenario:

  • With iCloud Photo Library enabled, he makes sure all his
    media is uploaded.
  • He disables iCloud Photo Library.
  • He deletes images from the library on his Mac.
  • He re-enables iCloud Photo Library.

His question is whether the new synchronization between his Mac
and iCloud will delete images. The answer: no. Deletions aren’t
tracked when iCloud Photo Library is disabled.

Generally, iCloud creates a superset without duplicates of
libraries as they’re added to iCloud Photo Library rather than
an exclusive intersection. That is, it only adds photos and
videos to the total synced set, no matter in which library they
appear, rather than creating a set that is only media shared
among all libraries.

When optimizing, are high-resolution photos
His second question is about the use of
Optimize Mac Storage in Photos > Preferences > iCloud
under iCloud Photo Library. “When my laptop runs out of space,
high-resolution photos will be deleted. Do I still have them
available in iCloud?” he asks. Another simple answer: yes.

mac911 optimize photos macos

Pick Optimize Mac Storage, and high-resolution versions get
purged automatically as storage is needed.

Your iCloud account will always maintain a high-resolution
version of any images and videos you initially sync via your
iOS device or Photos for macOS. With the optimized setting
enable on any of your hardware, the high-resolution version of
your media is only deleted and a thumbnail retained after that
version is uploaded to iCloud.

Now, I think this is risky, having a single copy. I have an
iMac, a MacBook, an iPhone, and an iPad all synced to the same
account. On my iMac, I retain full-resolution versions of all
media in iCloud Photo Library, because otherwise I would be
unable to have a full backup of my own. I’d be entirely relying
on Apple to maintain my full-resolution media. You can read my
philosophy on this and a strategy
in this column from last year

Can you store the library on an external
Finally, Pedro wonders about how to use an
external drive for his Photos library, and how that will work
with syncing to iCloud Photo Library. It’s very easy to copy
the library, and then set it as your System Photo Library,

as explained in this older column
. iCloud Photo Library can
only sync from the library you’ve anointed as your System Photo
Library, but that library can be resident on any drive you

But, yes and of course, you’ll have to make sure the drive is
available and mounted any time you want to access its library.
From the start and with no sign of changing, Apple can’t sync
to iCloud from multiple photo libraries. I’d hope the company
would consider more flexibility about marking multiple
libraries, including ones that might be offline at times.
There’s no additional cost for Apple, since users have to pay
for additional iCloud storage if they sync more photos and
media to it.

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